Theatre: Treats

Ostensibly a drawing comedy, it starts off feeling like a sitcom, thanks to its Habitatty set and a trio of actors more familiar from the small screen than the stage.

But it's canny casting, especially in the case of Marshall, whose presence casts a shadow over proceedings long after the curtain has come down.

Typecast as the loveable oaf in My Family and Love Actually, he here plays Dave, the arrogant, bullying and potentially abusive ex-boyfriend of Ann (Billie Piper), recently replaced by her new man Patrick (Laurence Fox), when the action begins.

The play charts his efforts to force himself back into Ann's flat and life by winning over first the audience, then Patrick, and finally Ann herself. And because we are used to liking him, Marshall succeeds in doing the first very quickly.

Yes, Dave's a bastard, who openly admits to arrogance, infidelities and giving Ann a split lip after her lunch meeting with a man called Justin. But he does so with such honesty and wit - "I objected to his name!" - that we laugh along with him.

Piper's Ann comes across as a bossy, joyless prude in comparison and for the first half, it is Dave's bravado and banter with gormless Patrick that gets the laughs.

But after the interval, things take a darker edge. Suffice to say that one scene offers such a shock that the whole audience - hitherto entranced by the sight of a semi-undressed Piper - gasps, as we are forced us to assess what has gone before, and acknowledge both the warning signs and our complicity.

Playwright Christopher Hampton gives each character a scene away from the triangle where they need no longer act, and it is here that the cast give their best performances.

Those who doubted Piper's career change (and I was one of them) may well be converted by her painful portrait of a woman choosing between the safe and predicatable and the dangerous but thrilling. Meanwhile, Fox will get the quietest praise for Patrick but he creates a character who is not only essential to the plot but touching in his vulnerability.

But this is Marshall's show and with it, he takes another step away from the canned-laughter echoes of My Family.

INTERVIEW: Playing the gooseberry

It's not much fun being the gooseberry. So perhaps Kris Marshall can be forgiven his gruffness when I call to discuss his latest role - opposite Billie Piper and Laurence Fox in a revival of Christopher Hampton's Treats.

Marshall, aka Nick from My Family, plays a bullying but charismatic journalist, Dave, who returns home to find his girlfriend (Piper) has finished with him and moved the office dullard (Fox) into their flat and bed.

The problem was that, over the weekend, the red tops had broken the story of a real life relationship forming between Piper and Fox, printing pics of the pair canoodling on Wimbledon Common near the house of Fox's actor father James.

So what has it been like rehearsing amidst this romance? Marshall answers abruptly: "I couldn't really comment on any of that." But he understands our interest, right? Art imitating life and all that. Cue stony silence.

It looks like we're going to have to talk about his fictional menage à trois instead. So Kris, your character Dave might be the dumpee, but better the bastard than the bore, hey?

"Well it goes a bit deeper than that," he corrects me. "Dave's an absolute shit - an egotistical reporter at a broadsheet - but what would you do if you came back to find your girlfriend had changed the locks and moved in a new man? Even if you did have it coming.

"It's interesting, when you read the play, it's quite an easy read. But it starts to creep up on you. We sat down for a good couple of weeks to flesh it out. It's a real, sneaky little play."

Marshall's face may be familiar from his screen rather than stage roles: My Family's bumbling oaf Nick Harper, Love Actually's bumbling oaf Colin Frissel and that older woman's younger guy in the BT ads.

But last year alone he found time to star in both The Hypochondriac at The Almeida and The Revenger's Tragedy at Southwark Playhouse.

"That was a very difficult play," he says of the Jacobean bloodbath, "but I found it liberating.

"I had nine weeks to find the part and it bleeds into your subconscious. I love filming but you rarely do more than two or three pages so it's easy to get fat and lazy. You have to psyche yourself up for a play. It's like being in a band - you need to do it live."

Even so, Marshall has four films out this year, the first of which - Death of a Funeral - boasts a Best of British cast that includes Jane Asher, who played Ann in the original 1975 production of Treats. Does Marshall finally feel Nick Harper is behind him?

"The public has a long memory - I left My Family over three years ago," he says.

"But it's getting better and, in the end, I don't really give a shit. Occasionaly you get some over-zealous fans but if they get too much, I just tell them to f*** off. Listen, if you're going to do the play, you gotta do your pay."

• Treats runs at Richmond Theatre until Saturday, February 17 and at the Garrick Theatre, London from Monday, February 20. Call 0870 060 6651 or visit richmondtheatre.net for tickets.